JP5327540B2 - Separator for lithium ion secondary battery and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator for a lithium ion secondary battery, capable of constructing a lithium ion secondary battery having better safety performance and high reliability. <P>SOLUTION: The separator for a lithium ion secondary battery includes a porous resin base material 200 and an insulating ceramic layer 300 applied to at least a first surface of the porous resin base material. The resin base material 200 has a porous polyethylene layer 210 as an internal layer and first and second porous polypropylene layers 220 and 230 as an external layer. The ceramic layer 300 includes at least an inorganic filler and a binder. The resin base material 200 includes a surface-modified layer 221 in an interface with the ceramic layer 300. The value of ratio &alpha;/&beta; is in a range of 0.015-0.055 in an infrared spectrum reflected and measured with respect to the modified surface, wherein &alpha; is an absorbance of C=C bond and &beta; is an absorbance of C-H bond. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a separator for a lithium ion secondary battery.

  In a lithium ion secondary battery including a non-aqueous electrolyte, a separator interposed between the positive electrode active material layer and the negative electrode active material layer prevents a short circuit due to contact between the two active material layers, and the separator By impregnating the electrolyte in the pores, it plays a role of forming an ion conduction path (conduction path) between the electrodes. A typical example of a separator used for a general lithium ion secondary battery is a single layer or multilayer porous film made of polyolefins such as polyester and polypropylene. Patent documents 1-6 are mentioned as technical literature about a separator of a rechargeable battery.

JP 2008-208511 A JP 2009-26733 A JP 2008-186722 A JP 2008-186721 A JP 2006-310302 A JP 2002-246000 A

  In order to ensure the safety of the battery and the device in which the battery is mounted, the lithium ion secondary battery separator has a certain temperature range (typically the separator) in addition to the short-circuit prevention function. When the temperature reaches the melting point (or softening point) of the battery, a function (shutdown function) that interrupts the ion conduction path to stop charging and discharging and prevents thermal runaway of the battery is required. In a general separator, the melting point (or softening point) of the polyolefin constituting the separator is a shutdown temperature, and when this temperature is reached, the fine pores of the separator are blocked by melting or softening, and between the electrodes. The charging / discharging is stopped by blocking the ion conduction. In recent years, the application range of lithium-ion secondary batteries has been rapidly expanding, and the use of lithium-ion secondary batteries in vehicles and other fields that require large-capacity power supplies has been studied. Further improvement is also demanded for its reliability.

  An object of the present invention is to provide a lithium ion secondary battery separator that is capable of constructing a lithium ion secondary battery that is more excellent in safety performance and high in reliability. Another object is to provide a method for producing such a separator.

  According to the conventional polyolefin separator, when a local short circuit occurs due to a film breakage or the like, there is a problem that the film breakage of the separator expands due to abnormal heat generation in that part, and the short circuit further expands therefrom. Focused on getting. In addition, since the separator is thermally contracted at the time of shutdown and the coating range of the separator is reduced, there is a problem that charging / discharging is not completely stopped, or both electrodes are in contact with each other and a new short-circuit portion is generated. We focused on what could happen. And the technique which avoids these malfunctions simultaneously was discovered, and this invention was completed.

  According to the present invention, a separator interposed between a positive electrode and a negative electrode of a lithium ion secondary battery is provided. The separator includes a porous resin base material having a porous polyethylene (PE) layer as an inner layer and first and second porous polypropylene (PP) layers as outer layers. Furthermore, an insulating ceramic layer provided on at least the first surface (one surface) of the porous resin substrate is provided. The ceramic layer includes at least an inorganic filler and a binder, and is typically provided on one side of the resin base material, but may be provided on both sides. The said resin base material contains a surface modification layer in the interface part (outer part containing an interface) with the said ceramic layer. The porous resin substrate including the surface modification layer is further subjected to reflection measurement by infrared spectroscopy (Infrared (IR) Spectroscopy) with respect to the modified surface (the surface having the surface modification layer). In the infrared spectrum (IR spectrum), the value α / β of the ratio between the intensity α of absorption due to stretching vibration of C = C bond and the intensity β of absorption due to symmetrical bending vibration of C—H bond in the methyl group (Hereinafter, also simply referred to as “C = C / C—H intensity ratio”) has a characteristic of being in the range of 0.015 to 0.055.

  Since the separator includes the resin base material having a PE layer and a PP layer having different melting points, a two-stage shutdown is possible. That is, according to such a separator, the shutdown temperature can be set in two stages: the melting point of PE (generally about 125 to 135 ° C.) and the melting point of PP (for example, about 155 to 165 ° C.). Further, since the PE layer having a low melting point is sandwiched between PP layers having a high melting point, the thermal contraction of the PE layer is suppressed by the PP layer that hardly contracts near the melting point of the PE (first shutdown temperature). be able to. In addition, since the ceramic layer having a small thermal shrinkage is provided even at the melting point of PP, the thermal shrinkage of the PP layer when reaching the melting point of PP (second shutdown temperature) can also be suppressed. Thereby, the malfunction by the thermal contraction of a separator can be avoided effectively and the reliability of a shutdown function can be improved.

  Moreover, the said separator becomes the aspect by which the said resin base material is protected by the said ceramic layer provided at least on the single side | surface, and can suppress generation | occurrence | production of the film breakage which can cause a local short circuit. In addition, since the melting point of the inorganic filler is much higher than the melting point of polyolefins, even when a local short circuit occurs, the ceramic layer causes a chain between the film breakage expansion and the short circuit expansion by the ceramic layer. Can be prevented. In addition, the thickness of the separator is increased by the ceramic layer, and the distance between the electrodes is increased by the thickness, which can contribute to the improvement of the reliability in preventing the short circuit. Furthermore, since the separator can also impregnate the pores in the ceramic layer with the electrolytic solution, the separator can hold more electrolytic solution as a whole. That is, according to the separator disclosed here, the above-described excellent safety performance can be realized while improving the ionic conductivity. In addition, the fact that the separator can hold a larger amount of electrolyte is particularly advantageous in a battery (such as a vehicle power supply battery) used in a mode in which high-rate charge / discharge is performed.

Furthermore, the resin base material includes a surface modification layer at an interface portion with the ceramic layer, and the resin base material including the surface modification layer has the IR spectrum characteristics as described above. The resin base material having such characteristics has extremely high adhesion to the ceramic layer as compared with that before the surface modification, while the deterioration of the base material due to the surface modification treatment (for example, a piercing strength test described later can be grasped). The decrease in strength.) Is small, and it may have sufficient strength as a separator substrate. That is, the separator has a sufficient strength, and the ceramic layer is appropriately cast on the resin base material and hardly peels off.
Therefore, the separator disclosed here is suitable as a separator for a lithium ion secondary battery that requires excellent safety performance and high reliability.

  In a preferred embodiment of the separator disclosed herein, the surface modified layer has fine pores having an average pore diameter of 0.12 μm or less. The resin base material having such a surface modified layer may be hard to be clogged with particles of various components (inorganic filler, binder, etc.) contained in the ceramic layer. Therefore, according to the three-layer resin base material provided with such a surface modified layer, a separator having more excellent ion permeability can be formed. The average pore diameter can be confirmed and measured (understood) by observing at least a part of the surface of the modified layer with an SEM (Scanning Electron Microscope) image or the like. In this specification, the average pore diameter is the average value of the diameters of the substantially circles (the major axis in the case of a substantially ellipse) when the pores are substantially circular (may be substantially elliptical). means. In the case where the pores have a substantially square shape (can be a substantially rectangular shape), it means an average value of one side of the substantially rectangular shape (or a long side in the case of a substantially rectangular shape).

  In another preferred embodiment, the separator has a peel strength measured by attaching an adhesive tape to the ceramic layer and peeling the ceramic layer from the substrate at a peel angle of 90 ° and a tensile speed of 100 mm / min. Is 3 N / m or more. The separator having such characteristics may be one in which the ceramic layer is more highly applied to the substrate. Therefore, a separator having excellent safety performance and higher reliability can be realized.

As another aspect of the present invention, a method of manufacturing any of the separators disclosed herein is provided. This manufacturing method includes the following steps (A) to (B).
(A) A step of performing a surface modification treatment on at least the first surface of the porous resin substrate to form a surface modification layer.
(B) A step of forming an insulating ceramic layer containing at least an inorganic filler and a binder on the surface modified layer.
Here, the porous resin base material has a porous PE layer as an inner layer and first and second porous PP layers as outer layers. In the step (A), the surface modification treatment is performed by the above-described C = C in the IR spectrum measured by reflection with respect to the modified surface of the substrate (the surface having the surface modified layer; the first surface). The C / C-H intensity ratio is carried out in a range of 0.015 to 0.055.

  Thus, by carrying out the surface modification treatment so that the C = C / C-H intensity ratio is in an appropriate range, the strength of the substrate is maintained at an appropriate level. Adhesiveness to the ceramic layer (which can also be grasped as anchoring property of the ceramic layer to the base material) can be remarkably improved. Therefore, according to this method, it is possible to provide a separator having excellent safety performance (short-circuit prevention function, shutdown function, etc.) and high reliability as described above.

In a preferred aspect of the method for producing a separator disclosed herein, the produced separator is wound together with a long sheet-like positive electrode and negative electrode to form a wound electrode body of a lithium ion secondary battery. It is a long sheet-like separator, comprising a long sheet-like porous resin base material having a porous polyethylene layer as an inner layer and first and second porous polypropylene layers as outer layers, (A) In the step, the corona discharge is irradiated at the surface by setting the irradiation amount of the corona discharge to 25 to 110 W · min / m ² when the long sheet-like porous resin substrate is fed at a feed rate of 10 m / min. A modified layer is formed. According to such a method, the above-mentioned C = C / CH intensity ratio can be suitably realized.

  As described above, the separator disclosed herein (including the separator manufactured by the method disclosed herein) can achieve excellent safety performance (short-circuit prevention function, shutdown function, etc.) with high reliability. Therefore, it is suitable as a separator for lithium ion secondary batteries for various applications. Therefore, according to the present invention, as another aspect, a lithium ion secondary battery including any of the separators disclosed herein is provided. In addition to such high safety performance, a battery equipped with a separator capable of holding a larger amount of electrolyte as described above is suitable for applications (such as in-vehicle use) used in a mode of performing high-rate charge / discharge. It is. Therefore, according to the present invention, there is further provided a vehicle including any one of the lithium ion secondary batteries disclosed herein. In particular, a vehicle (for example, an automobile) including such a lithium ion secondary battery as a power source (typically, a power source of a hybrid vehicle or an electric vehicle) is preferable.

It is sectional drawing which shows the separator which concerns on one Embodiment typically. 2 is an IR spectrum of a porous resin base material used for producing a separator according to Example 1. FIG. 6 is an IR spectrum of a porous resin base material used for producing a separator according to Example 5. It is a perspective view which shows typically the external shape of the lithium ion secondary battery provided with the separator of this invention. It is the VV sectional view taken on the line in FIG. It is a side view which shows typically the vehicle (automobile) provided with the lithium ion secondary battery of this invention.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  The separator provided by the present invention includes a porous resin base material having a multilayer structure and an insulating ceramic layer applied to at least a first surface thereof. The separator is typically formed in a long sheet shape, but is not limited to such a form, and can be processed into various shapes depending on the shape of the secondary battery in which the separator is used.

  The separator disclosed here may have, for example, a cross-sectional structure schematically shown in FIG. FIG. 1 is a configuration example of a separator having a ceramic layer on one side of a porous resin substrate. The separator 50 shown in FIG. 1 has a configuration in which a ceramic layer 300 is provided on the first surface (on the first PP layer 220) of the substrate 200. The substrate 200 is configured such that a porous PE layer 210 as an inner layer is sandwiched between porous PP layers 220 and 230 as outer layers. The PP layer 220 includes (includes) a surface modification layer 221 at an interface portion with the ceramic layer 300. Here, the PP layer 230 on which the ceramic layer is not provided may or may not have a surface modification layer. Typically, only the PP layer 220 provided with the ceramic layer has a surface modification layer. Although not shown, the separator disclosed herein may have a configuration in which the ceramic layer 300 is provided on both surfaces (on the first PP layer 220 and the second PP layer 230) of the substrate 200. In such a configuration, at least one of the PP layers 220 and 230 only needs to have a surface modification layer at the interface with the ceramic layer 300, and typically both the PP layers 220 and 230 have a surface modification layer. Have

  The porous resin base material is a ceramic of a porous resin film in which one PE layer is sandwiched between two PP layers (hereinafter, this film may be simply referred to as “resin film”). It can form by performing a surface modification process with respect to the surface (one side or both sides) which provides a layer. Hereinafter, the embodiment of the present invention will be described in detail with reference to the embodiment shown in FIG. 1, but is not intended to be limited to the embodiment.

The PE layer is preferably composed of PE having a melting point of about 120 ° C to 140 ° C (typically 125 ° C to 135 ° C). Examples of such PE include polyethylene generally referred to as high-density polyethylene or linear (linear) low-density polyethylene.
The first and second PP layers are preferably composed of PP having a melting point of about 150 to 170 ° C. (typically 155 to 165 ° C.). Examples of such polypropylene include isotactic polypropylene and syndiotactic polypropylene. The melting points of both PP layers may be the same or different. Typically, the melting points of both PP layers are approximately the same.

  As said resin film, what was uniaxially stretched or biaxially stretched and processed into porosity is used. Among these, a porous resin film that is uniaxially stretched in the longitudinal direction is preferable because it has an appropriate strength and has little heat shrinkage in the width direction. For example, according to a long sheet-shaped separator formed from such a longitudinally uniaxially stretched resin film, in the electrode body wound together with the long sheet-shaped positive electrode and negative electrode, longitudinal heat shrinkage is also suppressed. obtain. Therefore, a porous resin film uniaxially stretched in the longitudinal direction is suitable as a base material for a separator constituting such a wound electrode body.

  The total thickness (total thickness) of the resin film is preferably about 10 μm to 30 μm, and more preferably about 15 μm to 25 μm. The thicknesses of the PE layer and the first and second PP layers may be the same or different. Preferably, the thickness of the PE layer is about 4 μm to 10 μm, and the thicknesses of the first PP layer and the second PP layer are appropriately selected so that the total thickness is in the above range. If the total thickness of the resin film is too large, the ion conductivity of the formed separator may be lowered. If the total thickness is too small, the film may be broken by the surface modification treatment.

The total porosity of the resin film is preferably about 40 to 60% (more preferably 45 to 55%). The porosity of the first PP layer is preferably about 20 to 30%, and the porosity of the second PP layer is typically about the same as that of the first PP layer. The porosity of the PE layer is preferably higher than both PP layers, and can be, for example, about 50% to 80%. Thus, the separator which can hold | maintain sufficient amount of electrolyte solution can be formed by making the porosity of PE layer which is an inner layer high. Further, by using a PP layer having a low porosity as an external layer, the thermal shrinkage rate of the PP layer itself can be reduced, and the thermal shrinkage of PE can be more effectively reduced. If the total porosity is too low, the amount of electrolyte that can be held by the separator decreases, and the ionic conductivity may decrease. If the total porosity is too high, the strength may be insufficient and membrane breakage may occur.
The air permeability of the resin film is preferably about 200 to 500 seconds / 100 cc, for example. In addition, as the air permeability, a value measured according to JIS P8117 is adopted.

The first PP layer to which the ceramic layer is applied preferably has an average pore diameter of about 0.01 μm to 0.1 μm before surface modification. If the average pore diameter before the modification is too large, depending on the conditions of the surface modification treatment, the influence of the modification treatment extends to the deep part of the substrate, the substrate deteriorates, and the workability when producing the separator In some cases, the strength (such as puncture strength) of the manufactured separator tends to decrease. If the average pore diameter before modification is too small, the separator may not have sufficient ion permeability.
The average pore diameter of the second PP layer is preferably substantially the same as that of the first PP layer. Moreover, it is preferable that the average pore diameter of PE layer is larger than both PP layers in order to ensure a higher porosity.
As said resin film, the commercial item provided with the above characteristics may be used as it is, and what was manufactured in accordance with the conventionally well-known method may be used.

  The surface modification layer can be formed by subjecting the surface of the first PP layer of the resin film to a surface modification treatment such as corona discharge treatment or plasma discharge treatment. From the viewpoint of suppressing deterioration of the substrate due to the surface modification treatment, corona discharge treatment that can be performed under milder conditions is preferable.

The surface modification treatment is performed by using a C = C / C—H intensity ratio (C = C bond absorbance α and C—H bond) in an IR spectrum measured by reflection on the modified surface of the porous resin substrate. Is carried out so that the ratio α / β of the ratio to the absorbance β is in the range of about 0.15 to 0.55 (preferably 0.2 to 0.5). For example, when a surface modified layer is formed by corona treatment discharge, using a general corona surface treatment apparatus, the output, treatment time, and feed are set so that the C = C / C—H intensity ratio falls within the above range. What is necessary is just to set speed etc. suitably. For example, the C = C / C−H intensity is obtained by irradiating the corona discharge so that the irradiation amount of the corona discharge is 25 to 110 W · min / m ² (preferably 30 to 100 W · min / m ² ). The ratio can be in the above range.
In this specification, as the absorbance α of the C═C bond, the peak intensity (peak top) appearing in the vicinity of 1630 cm ⁻¹ due to the absorption due to the stretching vibration of the C═C bond is adopted. Further, the absorbance β of the C—H bond is the intensity of the peak appearing in the vicinity of 1375 cm ⁻¹ due to the absorption due to the symmetrical bending vibration of the three C—H bonds of the methyl group (side chain of PP). Top) shall be adopted. The IR measurement is performed on a surface having a surface modified layer by a reflection measurement method (for example, an ATR method (attenuated total reflection method)). Moreover, as each said intensity | strength, the value of each peak top correct | amended by making a base line into zero is employ | adopted. The light absorption due to the stretching vibration of the C═C bond is not seen in the IR spectrum of the resin film before modification, but newly appears in the IR spectrum after modification. This is considered to be due to the fact that hydrogen desorption occurs by the surface modification treatment and a C═C bond is generated.

  The surface modified layer preferably has an average pore size (that is, an average pore size after modification of the first PP layer) of about 0.01 μm to 0.12 μm. If the average pore diameter after modification is too large, the pores will be clogged by particles of various components (inorganic filler, binder, etc.) contained in the ceramic layer forming material, and ion permeability May be significantly impaired. The average pore diameter after the modification can be realized, for example, by performing a corona discharge treatment with the above settings using a resin film having an average pore diameter before modification of about 0.01 μm to 0.1 μm.

  The ceramic layer can be formed by applying (typically applying) a ceramic layer forming material on the surface modified layer and drying it. As the ceramic layer forming material, a material in which an inorganic filler and a binder are dissolved or dispersed in an appropriate solvent can be used.

As said inorganic filler (filler), the particle | grains which consist of an inorganic compound with high electrical insulation and melting | fusing point remarkably higher than the melting | fusing point of the said PP layer (for example, about 190 degreeC or more) can be used. For example, one or more inorganic compounds selected from oxide ceramics such as titania (titanium oxide; TiO ₂ ), alumina, silica, magnesia, zirconia, zinc oxide, iron oxide, ceria, yttria, etc. are in the form of particles. The one adjusted to can be used. Particularly preferred inorganic compounds include titania and alumina. The primary particle diameter of the inorganic compound particles is preferably larger than the average pore diameter of the surface modified layer, and can be, for example, about 0.15 μm to 2 μm (more preferably 0.2 μm to 1.5 μm). . The specific surface area is preferably about ² to 13 m ² / g.

  The binder is not particularly limited as long as it can function as a binder, but it is preferable to use a resin containing a functional group capable of hydrogen bonding (hydrogen-bonding functional group; —COOH, —OH, etc.). According to such a binder, the hydrogen bonding functional group is hydrogen bonded to the hydrogen bonding functional group of the surface modified layer (which can be introduced by surface modification treatment), so that the ceramic layer with respect to the base material is bonded. Throwing ability can be improved. Specific examples of such resin binders include cellulose resins such as carboxymethylcellulose (CMC); acrylic resins containing hydrogen bonding functional groups in the side chains; fluorine resins such as polyvinylidene fluoride (PVDF); It is done. These binders can be used alone or in combination of two or more. For example, a combination of a cellulose resin such as CMC and an acrylic resin can be preferably used. The average particle diameter of these binders is preferably larger than the average pore diameter of the surface modified layer, and typically about 0.09 μm to 0.15 μm is used.

  The form of the binder to be blended in the ceramic layer forming material is not particularly limited, and a particulate (powder) form may be used as it is, or a solution or emulsion prepared may be used. Two or more kinds of binders may be used in different forms. For example, a powdery or solution (aqueous solution) CMC and an emulsion acrylic resin can be used in combination. When an emulsion binder is used, the viscosity may be appropriately selected based on a desired solid content concentration (NV) of the ceramic layer forming material, handleability, and the like.

As a blending ratio of the inorganic filler and the binder, the mass ratio (NV basis) is preferably about 94: 6 to 99: 1. If the blending amount of the binder is too small, the anchoring property of the ceramic layer and the strength (shape retention) of the ceramic layer itself may be deteriorated, resulting in defects such as cracks and peeling. If the amount of the binder is too large, the surface modified layer may be clogged, or the ceramic layer may have insufficient porosity, which may reduce the ion permeability of the separator.
The NV of the ceramic layer forming material is preferably about 20 to 50%.

The solvent for dissolving or dispersing these components is not particularly limited, and is appropriately selected from, for example, water, alcohols such as ethanol, N-methylpyrrolidone (NMP), toluene, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and the like. Can be used. In the case of an aqueous solvent (typically water), the surface modification as described above is particularly effective, and the wettability of the surface to which the ceramic layer forming material is applied is improved, so that an aqueous solution or water The repellency of the dispersion can be prevented.
For the ceramic layer forming material, a surfactant, a wetting agent, a dispersing agent, a thickening agent, an antifoaming agent, and a pH adjustment are applied to the ceramic layer forming material as long as the function of the separator and the performance of the secondary battery to be manufactured are not impaired. You may mix | blend various additives, such as an agent (an acid, an alkali, etc.).

  The method for applying the ceramic layer forming material to the surface modification layer is not particularly limited. For example, a die coater, gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, air knife coater, spray A coater, a brush coater, a screen coater or the like can be used.

The drying process after application can be performed by appropriately selecting a conventionally known method. For example, a method of holding and drying at a temperature lower than the melting point of the PE layer (for example, about 80 ° C. to 100 ° C.) or a method of holding and drying at a low temperature under reduced pressure can be used.
The thickness of the ceramic layer after drying is preferably about 1 μm to 12 μm (more preferably 2 μm to 8 μm). If the thickness of the ceramic layer is too large, the handleability and workability of the separator may be reduced, and defects such as cracks and peeling may easily occur. If the thickness is too small, the short-circuit prevention effect may be reduced, or the amount of electrolyte that can be retained may be reduced.

  According to the present invention, the effect of suppressing the thermal shrinkage of the separator itself can be obtained by applying the ceramic layer on the separator as compared with the aspect of applying the ceramic layer on either the positive or negative electrode or the active material layer of both electrodes. Therefore, there are advantages that it is possible to prevent short circuit and more reliably realize charge / discharge stop at the time of shutdown.

  As described above, according to the technology disclosed herein, it is possible to form a separator that can exhibit excellent safety performance with high reliability and that has excellent nonaqueous electrolyte retention. Therefore, the matter disclosed herein is a method for producing any of the separators disclosed herein: forming a surface modified layer by subjecting the first PP layer of the resin film to surface modification treatment Step (A) in which the surface modification treatment is performed by comparing the C = C bond absorbance α and the C—H bond absorbance β in the IR spectrum measured for the modified surface of the substrate. The ratio value α / β (C = C / C—H intensity ratio) is carried out in the range of 0.015-0.055 (preferably 0.02-0.05); and A separator manufacturing method including a step (B) of forming an insulating ceramic layer containing at least an inorganic filler and a binder on the surface modification layer.

  In a preferred embodiment of the separator manufacturing method disclosed herein, the percentage of the piercing strength of the base material (after modification) relative to the piercing strength of the resin film (before modification) (hereinafter also referred to as the piercing strength ratio). .) Is 90% or more. Thus, by carrying out the surface modification treatment while maintaining the strength of the base material at a high level, the resin has excellent wettability to the ceramic layer forming material and adhesion to the ceramic layer, and has a suitable strength. A substrate can be obtained. Therefore, a separator having excellent safety performance and higher reliability can be provided. If the piercing strength ratio is too low, the film resistance of the formed separator may be lowered. The upper limit of the puncture strength ratio is not particularly limited, but normally, the puncture strength tends to be reduced by about 2% or more by such surface modification treatment, and can be about 98%. In addition, as the puncture strength, a value measured by the method described in the examples is adopted.

  As described above, the separator disclosed herein has high energy density and higher safety performance because it has a reliable and excellent short-circuit prevention function and shutdown function, and excellent nonaqueous electrolyte retention. Is suitable as a separator for lithium ion secondary batteries. Therefore, according to the present invention, there is further provided a lithium ion secondary battery including any separator disclosed herein (including a separator manufactured by the method disclosed herein).

  The lithium ion secondary battery disclosed herein includes an electrode body having positive and negative electrodes capable of occluding and releasing lithium ions together with any of the separators disclosed herein, and a lithium salt as a supporting salt in an organic solvent (non- A non-aqueous electrolyte solution contained in an aqueous solvent).

  Hereinafter, with reference to the drawings, for a lithium ion secondary battery to which the separator disclosed herein is applied, an electrode body including the separator 50 (FIG. 1) and a non-aqueous electrolyte are accommodated in a rectangular battery case. The lithium ion secondary battery 100 (FIG. 4) of the embodiment thus described will be described in more detail as an example, but the application target of the present invention is not intended to be limited to such an embodiment. That is, the shape of the lithium ion secondary battery including the separator according to the present invention is not particularly limited, and the battery case, electrode body, and the like are appropriately selected in terms of material, shape, size, and the like according to the application and capacity. be able to. For example, the battery case may have a rectangular parallelepiped shape, a flat shape, a cylindrical shape, or the like. In addition, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted or simplified. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

  As shown in FIGS. 4 and 5, the battery 100 according to this embodiment includes a wound electrode body 20 and a flat box-shaped battery case 10 corresponding to the shape of the electrode body 20 together with an electrolyte solution (not shown). It can be constructed by being housed inside the opening 12 and closing the opening 12 of the case 10 with a lid 14. The lid body 14 is provided with a positive terminal 38 and a negative terminal 48 for external connection so that a part of the terminals protrudes to the surface side of the lid body 14.

As the supporting salt contained in the nonaqueous electrolytic solution, a lithium salt used as a supporting salt in a general lithium ion secondary battery can be appropriately selected and used. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, LiCF ₃ SO _{3 and the} like. These supporting salts can be used alone or in combination of two or more. A particularly preferred example is LiPF ₆ . The nonaqueous electrolytic solution is preferably prepared so that the concentration of the supporting salt is within a range of 0.7 to 1.6 mol / L, for example.

  As said non-aqueous solvent, the organic solvent used for a general lithium ion secondary battery can be selected suitably, and can be used. Particularly preferred non-aqueous solvents include carbonates such as ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and propylene carbonate (PC). These organic solvents can be used alone or in combination of two or more.

  The electrode body 20 includes a positive electrode sheet 30 in which a positive electrode active material layer 34 is formed on the surface of a long sheet-like positive electrode current collector 32, and a negative electrode active material layer on the surface of a long sheet-like negative electrode current collector 42. The negative electrode sheet 40 on which the electrode 44 is formed is rolled up with two long sheet-like separators 50, and the obtained wound body is crushed from the side surface and ablated to form a flat shape. ing.

  Any separator disclosed herein can be used as the separator 50. The separator 50 is interposed between the positive electrode sheet 30 and the negative electrode sheet 40 and is disposed so as to be in contact with the positive electrode active material layer 34 of the positive electrode sheet 30 and the negative electrode active material layer 44 of the negative electrode sheet 40. Then, by impregnating the ceramic layer 300 of the separator 50 and the pores of the resin base material 200 with the electrolyte solution, an ion conduction path (conduction path) between the electrodes can be formed. When a separator having a ceramic layer on one side is used as the separator 50, the direction in which the ceramic layer is arranged is not particularly limited.

  The positive electrode sheet 30 is formed such that the positive electrode active material layer 34 is not provided (or removed) at one end portion along the longitudinal direction, and the positive electrode current collector 32 is exposed. Similarly, the negative electrode sheet 40 to be wound is not provided with (or removed from) the negative electrode active material layer 44 at one end along the longitudinal direction so that the negative electrode current collector 42 is exposed. Is formed. Then, the positive electrode terminal 38 and the negative electrode terminal 48 are joined to the exposed end portion of the positive electrode current collector 32 and the exposed end portion of the negative electrode current collector 42, respectively. The positive electrode sheet 30 or the negative electrode sheet 40 is electrically connected. The positive and negative terminals 38 and 48 and the positive and negative current collectors 32 and 42 can be joined by, for example, ultrasonic welding, resistance welding, or the like.

  The positive electrode active material layer 34 includes, for example, a paste or slurry composition (positive electrode mixture) in which a positive electrode active material is dispersed in an appropriate solvent together with a conductive material, a binder (binder), and the like as necessary. It can preferably be produced by applying to the positive electrode current collector 32 and drying the composition.

As the positive electrode active material, a material capable of inserting and extracting lithium is used, and one or more of materials conventionally used in lithium ion secondary batteries (for example, an oxide having a layered structure or an oxide having a spinel structure) are used. It can be used without any particular limitation. Examples thereof include lithium-containing composite oxides such as lithium nickel composite oxides, lithium cobalt composite oxides, lithium manganese composite oxides, and lithium magnesium composite oxides.
Here, the lithium nickel-based composite oxide is an oxide having lithium (Li) and nickel (Ni) as constituent metal elements, and at least one other metal element (that is, Li and nickel) in addition to lithium and nickel. An oxide containing a transition metal element other than Ni and / or a typical metal element) as a constituent metal element at a rate equivalent to or less than nickel in terms of the number of atoms (typically less than nickel) It means to include. Examples of the metal element other than Li and Ni include, for example, cobalt (Co), aluminum (Al), manganese (Mn), chromium (Cr), iron (Fe), vanadium (V), magnesium (Mg), and titanium (Ti ), Zirconium (Zr), niobium (Nb), molybdenum (Mo), tungsten (W), copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), lanthanum (La) And one or more metal elements selected from the group consisting of cerium (Ce). The same meaning applies to lithium cobalt complex oxides, lithium manganese complex oxides, and lithium magnesium complex oxides.
Further, an olivine type lithium phosphate represented by the general formula LiMPO ₄ (M is at least one element of Co, Ni, Mn, and Fe; for example, LiFePO ₄ , LiMnPO ₄ ) is used as the positive electrode active material. Also good.
The amount of the positive electrode active material contained in the positive electrode mixture can be selected as appropriate, and can be, for example, about 80 to 95% by mass.

As the conductive material, a conductive powder material such as carbon powder or carbon fiber is preferably used. As the carbon powder, various carbon blacks such as acetylene black, furnace black, ketjen black, and graphite powder are preferable. A conductive material can be used alone or in combination of two or more.
What is necessary is just to select suitably the quantity of the electrically conductive material contained in a positive electrode compound material according to the kind and quantity of a positive electrode active material, for example, can be about 4-15 mass%.

As the binder, for example, a water-soluble polymer that dissolves in water, a polymer that disperses in water, a polymer that dissolves in a non-aqueous solvent (organic solvent), and the like can be appropriately selected and used. Moreover, only 1 type may be used independently and 2 or more types may be used in combination.
Examples of the water-soluble polymer include carboxymethylcellulose (CMC), methylcellulose (MC), cellulose acetate phthalate (CAP), hydroxypropylmethylcellulose (HPMC), hydroxypropylmethylcellulose phthalate (HPMCP), and polyvinyl alcohol (PVA). It is done.
Examples of the water-dispersible polymer include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and ethylene-tetra. Fluorine resin such as fluoroethylene copolymer (ETFE), vinyl acetate copolymer, styrene butadiene block copolymer (SBR), acrylic acid-modified SBR resin (SBR latex), rubbers such as gum arabic, etc. It is done.
Examples of the polymer dissolved in the non-aqueous solvent (organic solvent) include, for example, polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyethylene oxide (PEO), polypropylene oxide (PPO), and polyethylene oxide-propylene oxide copolymer. (PEO-PPO) and the like.
What is necessary is just to select the addition amount of a binder suitably according to the kind and quantity of a positive electrode active material, for example, can be about 1-5 mass% of the said positive electrode compound material.

  For the positive electrode current collector 32, a conductive member made of a metal having good conductivity is preferably used. For example, aluminum or an alloy containing aluminum as a main component can be used. The shape of the positive electrode current collector 32 may vary depending on the shape of the lithium ion secondary battery, and is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape. . In the present embodiment, a sheet-like aluminum positive electrode current collector 32 is used, and can be preferably used for the lithium ion secondary battery 100 including the wound electrode body 20. In such an embodiment, for example, an aluminum sheet having a thickness of about 10 μm to 30 μm can be preferably used.

  The negative electrode active material layer 44 includes, for example, a negative electrode current collector 42 made of a paste or slurry composition (negative electrode mixture) in which a negative electrode active material is dispersed in an appropriate solvent together with a binder (binder) and the like. And the composition can be preferably prepared by drying.

As the negative electrode active material, one type or two or more types of materials conventionally used in lithium ion secondary batteries can be used without any particular limitation. For example, a carbon particle is mentioned as a suitable negative electrode active material. A particulate carbon material (carbon particles) containing a graphite structure (layered structure) at least partially is preferably used. Any carbon material of a so-called graphitic material (graphite), non-graphitizable carbon material (hard carbon), easily graphitized carbon material (soft carbon), or a combination of these materials is preferably used. obtain. Among these, graphite particles such as natural graphite can be preferably used. Since the graphite particles can suitably occlude lithium ions as charge carriers, they are excellent in conductivity. Moreover, since the particle size is small and the surface area per unit volume is large, it can be a negative electrode active material more suitable for rapid charge / discharge (for example, high output discharge).
The amount of the negative electrode active material contained in the negative electrode mixture is not particularly limited, but is preferably about 90 to 99% by mass, more preferably about 95 to 99% by mass.

  As the binder, the same positive electrode as that described above can be used alone or in combination of two or more. What is necessary is just to select the addition amount of a binder suitably according to the kind and quantity of a negative electrode active material, for example, can be about 1-5 mass% of a negative electrode compound material.

  As the negative electrode current collector 42, a conductive member made of a metal having good conductivity is preferably used. For example, copper or an alloy containing copper as a main component can be used. In addition, the shape of the negative electrode current collector 42 may vary depending on the shape of the lithium ion secondary battery and the like, and thus is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape. possible. In the present embodiment, a sheet-like copper negative electrode current collector 42 is used, and can be preferably used for the lithium ion secondary battery 100 including the wound electrode body 20. In this embodiment, for example, a copper sheet having a thickness of about 5 μm to 30 μm can be preferably used.

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples. In the following description, “parts” and “%” are based on mass unless otherwise specified.

[Preparation of separator]
<Example 1>
A PP-PE-PP three-layer film having a thickness of 20 μm (a porosity of 47%, an air permeability of 400 seconds / 100 cc, a PP layer average pore diameter of 0.02 μm) (surface unmodified) and a resin base material according to Example 1 did.
Titanium oxide (TiO ₂ ) (primary particle size of 0.25 μm, specific surface area of 7-10 m ² / g), CMC, and acrylic resin are such that their mass ratio is 97: 1: 2 and NV is 40%. A ceramic layer forming material was prepared by dispersing in ion exchange water.
The ceramic layer-forming material is applied and dried to the first PP layer (unmodified surface) of the resin base material so that the thickness after drying is 4 μm, and a ceramic layer is formed. It was.

<Example 2>
For the surface of the first PP layer of the base material of Example 1, using a corona surface treatment apparatus (model “AGI030” manufactured by Kasuga Denki Co., Ltd.), the irradiation amount of corona discharge is 30 W · min / m ² . The resin base material of Example 2 was obtained by irradiating corona discharge at a feed rate of 10 m / min, applying surface modification treatment to form a surface modification layer. A ceramic layer was formed on the surface modification layer of this substrate in the same manner as in Example 1 to obtain a separator according to Example 2.
<Example 3>
A resin base material according to Example 3 was obtained in the same manner as in Example 2 except that the surface modification treatment was performed so that the dose of corona discharge was 40 W · min / m ² . A ceramic layer was formed in the same manner as in Example 2 except that this substrate was used, and a separator according to Example 3 was obtained.
<Example 4>
A resin substrate according to Example 4 was obtained in the same manner as in Example 2 except that the surface modification treatment was performed so that the irradiation dose of corona discharge was 50 W · min / m ² . A ceramic layer was formed in the same manner as in Example 2 except that this substrate was used, and a separator according to Example 4 was obtained.
<Example 5>
A resin substrate according to Example 5 was obtained in the same manner as in Example 2 except that the surface modification treatment was performed so that the irradiation dose of corona discharge was 100 W · min / m ² . A ceramic layer was formed in the same manner as in Example 2 except that this substrate was used, and a separator according to Example 5 was obtained.
<Example 6>
A resin base material according to Example 6 was obtained in the same manner as in Example 2 except that the surface modification treatment was performed so that the irradiation dose of corona discharge was 120 W · min / m ² . A ceramic layer was formed in the same manner as in Example 2 except that this substrate was used, and a separator according to Example 6 was obtained.

  The following measurements were performed for each resin substrate of Examples 1-6. The results are shown in Table 1.

[IR spectrum analysis]
A sample obtained by cutting the resin base material of each example into 50 mm × 50 mm was used as a sample, and an ATR (model “FTS-55A”, manufactured by Bio Rad Digilab Inc.) using an FT-IR apparatus (Fourier transform infrared spectrometer). IR measurement was performed on the modified surface of each substrate by the Attenuated Total Reflection method. From the obtained FTIR-ATR spectrum, the C = C / CH intensity ratio (absorbance near 1630 cm ⁻¹ / absorbance near 1375 cm ⁻¹ ) was determined as described above. Among these, the IR spectrum of the base material of Example 1 is shown in FIG. 2, and the IR spectrum of the base material of Example 5 is shown in FIG. In addition, as shown in FIG. 3, the IR spectra of the base materials of Examples 2 to 6 were modified in surface as well as absorption (near 1630 cm ⁻¹ ) indicating the presence of C═C bond. Absorption due to C═O bond (near 1708 cm ⁻¹ ) and O—H bond (near 3400 cm ⁻¹ ) was observed.

[Puncture strength ratio]
Using a compression tester (model “KES-G5” manufactured by Kato Tech Co., Ltd.) for each resin base material, the fixed base material surface is 1.0 mm in diameter at a speed of 100 mm / min, and the tip has a radius. The load (gf) until the needle penetrates with a 0.5 mm hemispherical needle was measured, and the maximum value was defined as the puncture strength. The percentage of the piercing strength of each example with respect to the piercing strength of the untreated substrate (base material of Example 1) was defined as the piercing strength ratio (%).

[Average pore diameter of ceramic layer application surface]
The average pore diameter (μm) was determined from an SEM image including a range of 6 μm × 6 μm on the surface of the first PP layer of each resin substrate (that is, the surface modified layer surface for the substrates of Examples 2 to 6).

About the separator of Examples 1-6, the peeling strength of the interface of the base material and a ceramic layer was measured as follows. The results are also shown in Table 1.
[Peel strength]
Each separator was cut into 10 mm × 100 mm, and an adhesive tape was bonded to the ceramic layer to prepare a test piece. After holding this test piece at 23 ° C. for 1 hour, using a tensile tester (manufactured by Shimadzu Corporation, model “AG-50kNX”) in an environment of 23 ° C. and 50% relative humidity, a peeling angle of 90 °, The stress when the adhesive tape-attached ceramic layer was peeled from the substrate at a tensile speed of 100 mm / min was measured, and the maximum value was defined as peel strength (N / m).

[Production of battery]
<Example 7>
Using the separator of Example 3, a prismatic lithium ion secondary battery with a capacity of 5 Ah was produced as follows.
As the positive electrode mixture, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (positive electrode active material), acetylene black (conductive material), and PVDF (binder) have a mass ratio of 87:10: 3 was mixed and dispersed in NMP such that NV was 50% to prepare a slurry composition. The positive electrode mixture was applied to both sides of an aluminum foil (positive electrode current collector) having a thickness of 15 μm and dried, and then pressed to obtain a positive electrode sheet.
As a negative electrode mixture, natural graphite (negative electrode active material), CMC, and SBR are mixed so that the mass ratio thereof is 98: 1: 1, and dispersed in ion-exchanged water so that NV is 46%. Thus, a slurry-like composition was prepared. The negative electrode mixture was applied to both sides of a 10 μm thick copper foil (negative electrode current collector), dried, and then pressed to obtain a negative electrode sheet.
LiPF ₆ was dissolved in a mixed solvent containing EC, DMC, and EMC at a volume ratio of 3: 3: 4 to a concentration of 1 mol / L to prepare a non-aqueous electrolyte.
The positive electrode sheet and the negative electrode sheet cut out to appropriate sizes are overlapped and wound together with the separator of Example 3 impregnated with the electrolytic solution, and the obtained wound electrode body is crushed into a flat shape to form a square container. Accommodated. The electrolyte solution was poured into this container, and the container was sealed to construct a lithium ion secondary battery. The operation of charging the battery to 4.1 V at a rate of 1/10 C at a temperature of 25 ° C. and the operation of discharging to 3.0 V at the same rate were repeated three times alternately. Next, the battery is charged at a rate of 1 C until the voltage reaches 4.1 V, and then charged at 4.1 V until the SOC (State of Charge) reaches 100% (that is, the amount of charge corresponding to 5 Ah). The lithium ion secondary battery which concerns on Example 7 was obtained by performing constant voltage (CC-CV) charge.

<Example 8>
A resin base material was obtained in the same manner as in Example 3 except that a PE single layer film having a thickness of 20 μm (porosity 40%, air permeability 290 seconds / 100 cc, average pore diameter 0.012 μm) was used. Using this substrate, a ceramic layer was formed in the same manner as in Example 1 to obtain a separator according to Example 8. A lithium ion secondary battery according to Example 8 was obtained in the same manner as Example 7 except that this separator was used.
<Example 9>
As the separator, the resin substrate of Example 1 (surface unmodified) was used as it was. Otherwise, in the same manner as Example 7, a lithium ion secondary battery according to Example 9 was obtained.
<Example 10>
As a separator, a PE single-layer film having a thickness of 20 μm (a PE single-layer film (surface unmodified) used for preparing the resin base material of Example 8) was used. Others were the same as in Example 7, and the lithium ion secondary battery according to Example 10 was obtained.
<Example 11>
The ceramic layer forming material of Example 2 is applied and dried on the first surface (first active material layer surface) of the positive electrode sheet of Example 7 so that the thickness after drying is 4 μm, and the ceramic layer is formed on one surface. A positive electrode sheet was prepared. Similarly, using the negative electrode sheet of Example 7, a negative electrode sheet having a ceramic layer on one side was produced. A lithium ion secondary battery according to Example 11 was obtained in the same manner as Example 9 (that is, using the separator of Example 9) except that these positive and negative electrode sheets were used.
<Example 12>
A lithium ion secondary battery according to Example 12 was obtained in the same manner as in Example 10 (that is, using the separator of Example 10) except that the positive electrode sheet and the negative electrode sheet with the ceramic layer of Example 11 were used.

  The following measurements were made for each battery of Examples 7-12. The results are shown in Table 2.

[Overcharge test]
Each battery adjusted to 100% SOC was charged to 20 V at a rate of 10 C at a temperature of 60 ° C., and then charged to 20% SOC until reaching SOC 200%, and CC-CV charging was performed. At this time, thermocouples were attached to a plurality of locations of each battery outer can, the temperature of the battery cell was measured, and the maximum temperature among them was recorded as the maximum overcharge temperature (° C.).

[Low temperature output measurement]
Each battery is adjusted to SOC 60% (voltage 3.7V) and discharged at a constant power (W) of 40W, 60W, 80W and 100W at a temperature of -30 ° C. The time required (discharge seconds) was measured. The power value (W) in the constant power discharge is plotted against the number of discharge seconds, and the power value at which the discharge time is 2 seconds (that is, discharge from SOC 60% at −30 ° C. to SOC 0% in 2 seconds) Output) was determined as the discharge output at −30 ° C.

  As shown in Table 1, the separators of Examples 2 to 5 using a three-layer resin base material having a C = C / C-H strength ratio in the range of 0.015 to 0.055 are pierced strength ratios. Was 90% or more (that is, the rate of decrease in puncture strength before and after modification was 10% or less), and there was little deterioration of the substrate due to the surface modification treatment. In addition, the separators of Examples 2 to 5 have a peel strength at the interface between the base material and the ceramic layer of about 2 to 3 times that of the separator of Example 1 using an unmodified resin base material. And the anchoring property (throwing degree) of the ceramic layer with respect to the said base material was remarkably high. Furthermore, the resin base materials used in the separators of Examples 2 to 5 each had an average pore diameter of the surface modified layer of 0.12 μm or less, and had a surface shape in which clogging due to ceramic layer components hardly occurred. Was confirmed. On the other hand, the separator of Example 6 had a surface shape in which the average pore diameter exceeded 0.12 μm and clogging easily occurred.

  Moreover, as shown in Table 2, the battery of Example 7 using the separator of Example 3 has a maximum overcharge temperature of 163 ° C., and charging / discharging completely stops near the melting point of PP, and the shutdown function is defective. The results were found to work without any problems. Further, the battery of Example 7 showed a high output even at a low temperature of −30 ° C., ie, −30 ° C. discharge output of 180 W. On the other hand, the battery of Example 8 using a separator with a ceramic layer provided by applying surface modification to a PE single-layer base material has an overcharge maximum temperature of 178 ° C., which is higher than the melting point of PE constituting the base material. The result was extremely high, indicating that the charge and discharge continued partially even after the shutdown function was activated at the melting point of PE, and the temperature in the battery rose. The battery of Example 8 also had a −30 ° C. discharge output lower than that of Example 7. In addition, in the batteries of Examples 9 and 10 using the separator without the ceramic layer, charging and discharging partially continued after shutdown, and the maximum overcharge temperature was about 30 to 50 ° C. higher than the battery of Example 7. . Further, the -30 ° C. discharge output was also lower by 5 W or more. Similarly, the batteries of Examples 11 and 12 in which the separators similar to those of Examples 9 and 10 are used and the ceramic layers are provided on both electrode sheets also have a maximum overcharge temperature of about 20 to 30 compared to the battery of Example 7. ℃ was high. In addition, the batteries of Examples 11 and 12 had a discharge output of −30 ° C. lower than the battery of Example 7 by about 60 W or more.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

DESCRIPTION OF SYMBOLS 1 Vehicle 20 Winding electrode body 30 Positive electrode sheet 32 Positive electrode collector 34 Positive electrode active material layer 38 Positive electrode terminal 40 Negative electrode sheet 42 Negative electrode current collector 44 Negative electrode active material layer 48 Negative electrode terminal 50 Separator 100 Lithium ion secondary battery 200 Resin group Material 210 Polyethylene layer 220, 230 Polypropylene layer 221 Surface modification layer 300 Ceramic layer

Claims (4)

A method for producing a long sheet-shaped separator wound together with a long sheet-shaped positive electrode and a negative electrode to constitute a wound electrode body of a lithium ion secondary battery :
(A) Corona discharge is applied to at least the first surface of a long sheet-like porous resin substrate having a porous polyethylene layer as an inner layer and first and second porous polypropylene layers as outer layers. forming a surface modification layer subjected to a surface modification treatment by, where, before Symbol surface modification treatment, the infrared spectrum reflected measured for reforming surface of the porous resin substrate The long sheet-like porous resin base material so that the ratio α / β of the absorbance α of C = C bond and the absorbance β of C—H bond in the range of 0.015 to 0.055 Carried out by setting the irradiation amount of the corona discharge to 25 to 110 W · min / m ² at a feed rate of 10 m / min ; and
(B) forming an insulating ceramic layer on the surface modified layer;
A separator manufacturing method for a lithium ion secondary battery. The average pore diameter before the surface modification treatment of the first and second porous polypropylene layers is 0.01 μm to 0.1 μm, and the average pore diameter of the surface modification layer after the surface modification treatment is 0.12 μm. The separator manufacturing method of Claim 1 which is the following. A lithium ion secondary battery comprising a wound electrode body in which a long sheet-like positive electrode and a negative electrode and a long sheet-like separator are wound,
A lithium ion secondary battery provided with a separator manufactured by carrying out the manufacturing method according to claim 1 or 2 as the separator . A vehicle comprising the battery according to claim 3 .

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